This invention relates generally to tone detection on full-duplex communication channels, such as telephone lines, and more particularly to methods and apparatus for reducing talk-off and cut-through in the detection of signaling tones, such as DTMF tones.
A number of different types of telephonic equipment communicate control information by sending and detecting signaling tones. The Dual-Tone, Multi-Frequency (DTMF) standard is an extensively-used standard for some of these signaling tones. It defines 16 different tone pairs (digits) that are each made up of a low tone and a high tone. The low tone can be a 697 Hz, 770 Hz, 852 Hz, or 941 Hz tone, and the high tone can be a 1209 Hz, 1336 Hz, 1477 Hz, or 1633 Hz tone. A variety of different kinds of circuits exist to detect these tone pairs, including digital filters.
Tone detectors sometimes suffer from xe2x80x9ctalk-off.xe2x80x9d Talk-off occurs when a signal, such as person""s voice, is decoded as a tone. This can happen when part of the telephone system is waiting for a signaling tone and sounds in the signal coincidentally include the two tones defined as one of the DTMF tone pairs.
Some tone detectors can also fail to detect tones because of what is known as xe2x80x9ccut-through.xe2x80x9d DTMF detectors that suffer from cut-through generally detect tones by comparing the magnitude of the energy in the tone frequency ranges with the magnitude of the energy outside of the tone ranges. These detectors may miss signaling tones in the presence of other sounds on the telephone line.
In one general aspect, the invention features a communication signaling tone detection system that includes an outgoing signaling tone detector responsive to an output from a first station to a communication channel. An incoming signaling tone detector is responsive to an input to the first station from the communication channel. A sensitivity control input of the incoming signaling tone detector is responsive to a detection output of the outgoing signaling tone detector.
In preferred embodiments, the incoming and outgoing signal tone detectors can be DTMF detectors. A CODEC can be operatively connected between an output of the outgoing signaling tone detector, an input of the incoming signaling tone detector, and the communication channel. The communication channel can be connected to an analog public network telephone line. The outgoing signaling tone detector can be less sensitive than the incoming signaling tone detector. The signaling tone detectors can both be implemented as digital filters. The detection output of the outgoing signaling tone detector can be operative to indicate which of a plurality of predetermined signaling tones the detector has received.
In another general aspect, the invention features a method of detecting signaling tones from a communication channel that includes detecting outgoing signaling tones in a communication stream transmitted from a first station over the communication channel to a second station, detecting incoming signaling tones in a communication stream transmitted from the second station over the communication channel to the first station, and altering at least one attribute of the step of detecting incoming signaling tones based on whether signaling tones are detected by the step of detecting outgoing signaling tones.
In preferred embodiments, the steps of detecting can detect DTMF tones as the signaling tones. The step of altering can decrease the sensitivity of the step of detecting when the outgoing signaling tones are detected by the step of detecting spurious signals. The step of altering can temporarily disable the step of detecting. The step of altering can invalidate a result of the step of detecting incoming signaling tones when a same signaling tone is detected by both the step of detecting outgoing signaling tones and the step of detecting incoming signals. The communication stream can be an audio stream. The step of detecting outgoing tones can be less accurate than the step of detecting incoming tones.
In a further general aspect, the invention features a communication signaling tone detection system that includes means for detecting outgoing signaling tones in a communication stream transmitted from a first station over the communication channel to a second station, means for detecting incoming signaling tones in a communication stream transmitted from the second station over the communication channel to the first station, and means for altering at least on attribute of the step of detecting incoming signaling tones based on whether outgoing signaling tones are detected by the means for detecting outgoing signaling tones.
In preferred embodiments, The means for detecting can detect DTMF tones as the signaling tones. The means for altering can include means for decreasing the sensitivity of the step of detecting when the outgoing signaling tones are detected by the means for detecting outgoing signals. The means for altering can include means for temporarily disabling the means for detecting incoming signals. The means for altering can include means for invalidating a result of the means for detecting incoming signals when a same signaling tone is detected by both the means for detecting outgoing signaling tones and the means for detecting incoming signaling tones. The means for detecting outgoing tones can be less accurate than the means for detecting incoming tones.
In another general aspect, the invention features a communication signaling tone detection system that includes a signal characteristic value detector responsive to a communication channel during a measurement period, threshold storage responsive to the signal characteristic value detector, and a threshold detector that is responsive to the threshold storage and to the communication channel during a detection period, and that has a signaling tone reporting output.
In preferred embodiments, the threshold detector can be a DTMF detector. The signal characteristic value detector can be an amplitude detector. The signal characteristic value detector can be a twist detector. The threshold detector can be operative to leave a margin between a threshold value stored by the signal characteristic detector and a detection threshold value. The signal characteristic detector and the threshold detector can be implemented using a digital signal processor.
In a further general aspect, the invention features a communication signaling tone detection system that includes means for measuring a characteristic of a signal while a signaling tone is present on the channel, and for defining a threshold based on the characteristic. The system also includes storage for storing the threshold, and signaling tone detection means responsive to the means for measuring and to the communication channel to detect when a signal on the communication channel exceeds the threshold.
In preferred embodiments, the signal tone detector can be a DTMF detector. The signal characteristic of the signaling tone can be an amplitude of the signaling tone. The signal characteristic of the signaling tone can be a twist value of the signaling tone. The signaling tone detector and the means for measuring and detecting can be implemented using a digital signal processor.
In another general aspect, the invention features a method of detecting signal tones from a communication channel that includes measuring a characteristic of a signal on the communication channel while a first signaling tone is present on the channel, adjusting a detection threshold based on the characteristic measured in the step of measuring, and detecting a second signaling tone according to the adjusted threshold.
In preferred embodiments, the steps of measuring and adjusting can measure and adjust an energy detection threshold. The steps of measuring and adjusting can measure and adjust a twist threshold. The step of measuring can take place while only the signaling tone is present on the communication channel. The method can further include the steps of setting up a first session on the communication channel before the step of measuring, shutting down the first session on the communication channel after the step of detecting, setting up a second session on the communication channel after the step of shutting, and repeating the steps of measuring, adjusting, and detecting after the step of setting up a second session.
In a further general aspect, the invention features a communication signaling tone detection system that includes an outgoing energy detector responsive to an output from a first station to an interface circuit for a communication channel, the outgoing signaling tone detector having a detection output, a incoming energy detector responsive to an input to the first station from the interface circuit, the incoming signaling tone detector having a sensitivity control input, a trans-hybrid loss measurement module responsive to the interface circuit, a trans-hybrid loss correction module responsive to the incoming signaling tone detector, to the outgoing signaling tone detector and to the trans-hybrid loss measurement module, and a signaling tone detector responsive to the trans-hybrid loss correction module.
In preferred embodiments, the incoming energy detector, the outgoing energy detector, and the trans-hybrid measurement module can be responsive to energy in each of a number of frequency bands. The incoming energy detector, the outgoing energy detector, and the trans-hybrid measurement module can be responsive to energy in each of a number of frequency bands defined by the DTMF standard. The trans-hybrid loss connection module can be operative without phase information. The trans-hybrid loss connection module and the signaling tone detector can both be implemented with a signal processor.
In another general aspect, the invention features a communication signaling tone detection system that includes means for measuring a communication parameter of a communication channel, means for adjusting the received signal parameter a signal received from the communication channel according to the measured communication parameter, and means for detecting signaling tones using the adjusted received signal parameter.
In preferred embodiments, the means for measuring can be for measuring trans-hybrid loss. The signal parameter can be signal energy and the means for adjusting can include means for correcting the signal energy for trans-hybrid loss. The communication parameter can be measured for each of a number of frequency bands. The means for measuring can measure the communication parameter for members of each of two groups of frequency bands defined by the DTMF standard. The system can include means for initiating the means for adjusting before sending an audio signal from a first station to a second station over the communication channel during which tones are to be detected from the second station at the first station.
In another general aspect, the invention features a method of detecting signal tones from a communication channel that includes measuring a communication parameter of the communication channel, measuring a signal parameter of a signal received from the communication channel, adjusting the received signal parameter according to the measured communication parameter, and detecting signaling tones using the adjusted received signal parameter.
In preferred embodiments, the communication parameter can be trans-hybrid loss. The signal parameter can be signal energy and the step of adjusting can include correcting the signal energy for trans-hybrid loss. The communication parameter can be measured for each of a number of frequency bands. The communication parameter can be measured for members of each of two groups of frequency bands defined by the DTMF standard. The step of adjusting can be initiated before sending an audio signal from a first station to a second station over the communication channel during which tones are to be detected from the second station at the first station. The step of measuring can take place during call set-up.
In a further general aspect, the invention features a communication signaling tone detection system that includes a tone filter having an input responsive to a source of communication signals, a full-duplex communication channel having a first end that has an input responsive an output of the tone filter, and a tone detector responsive to an output of the first end of the communication channel.
In preferred embodiments, the source of outgoing communication signals can include message storage. The tone filter can be constructed and adapted to filter signals from the source in real time. The tone filter can be constructed and adapted to filter signals from the source and store them for later transmission over the communication channel. The filter can be adapted to operate when the system has a predetermined resource availability level. The source can be connected to the communication channel via the filter. The filter can be adapted to filter all DTMF signal tone component frequencies from the source. The filter can have a control input responsive to the tone detector.
In another general aspect, the invention features a communication signaling tone detection system that includes means for filtering signal tone frequencies from communication signals to be transmitted on the communication channel from a first end to a second end, and means for detecting signal tones, including the tone frequencies received from the first end of the communication channel.
In preferred embodiments, the system can include a source of outgoing communication signals that include means for storing messages. The means for filtering can be for filtering signals in real time. The means for filtering can be for filtering signals and storing them for later transmission over the communication channel. The means for filtering can be for filtering all DTMF signal tone component frequencies from the signal. The means for filtering can be responsive to the means for detecting tones. The means for filtering and the means for detecting can be adapted to respectively filter and detect DTMF tones.
In a further general aspect, the invention features a method of detecting signal tones from a communication channel that includes filtering a signal in real time to eliminate at least one frequency component associated with signaling tones, sending a filtered signal resulting from the step of filtering out over a communication channel, and detecting signaling tones from the communication channel as the filtered signal is being sent over the communication channel.
In preferred embodiments, the step of filtering can take place as the signal is received from the communication channel. The step of filtering can take place as the signal is transmitted over the communication channel. The step of filtering can overlap with retrieval of the signal from storage. The step of filtering can take place when a predetermined amount of processing resources are available. The step of filtering and the step of detecting can be applied to all DTMF tone component frequencies.
In another general aspect, the invention features a method of detecting signal tones from a communication channel that includes detecting signaling tones in a signal, and selectively filtering a signal to eliminate at least one frequency component associated with signaling tones in response to detection of signaling tones in the signal by the step of detecting, and detecting signals from the selectively filtered signal. In preferred embodiments, the step of filtering and the step of detecting can be applied to DTMF tones.
Systems according to the invention may be advantageous in that they allow for reductions in talk-off, cut-through, or both. These reductions may allow a system to detect tones more reliably, or they may allow a system with particular computational capabilities to detect more tones with a similar level of accuracy.